The present invention relates to a method for attaching an insert at least partly composed of thermoplastic material in an opening into a hollow body having at least a portion thereof formed of a thermoplastic material for attachment of the insert. More specifically, the invention is related to a method and apparatus for mounting an insert having a thermoplastic mounting portion in the opening into a molded thermoplastic hollow body.
In accordance with prior art techniques for producing hollow bodies, such as drums or tanks, the body is usually completely fabricated and the insert is then attached using screws and, optionally, a sealing ring. Alternatively, the insert may be welded or glued to the outside of the body over an opening provided in the wall of the body for this purpose.
The foregoing methods are expensive due to the manual labor and expertise required to attach the insert to the hollow body. Also, an insert attached with such methods does not provide a sufficiently tight seal between the body and the insert, especially if the body is to be subjected to internal pressure during its use.
In rotational molding or casting techniques, the complex mold movements, high molding temperatures and long molding cycles are believed sufficiently severe to have heretofore substantially precluded automatic insert assembly techniques. For example, polyethylene drums having about a 2' diameter and a 4' height require about a 15 minute molding cycle at 500.degree. F.
In contrast with the foregoing relatively severe conditions of rotational molding, blow molding of similarly sized drums is done in a stationary mold apparatus using about a 5 minute cycle and a parison temperature of about 300.degree. F. Thus, it has been possible in blow molding techniques to mount an insert for the hollow body opening on the blow pin and, after blowing, to retract the blow pin to cause the insert to contact and fuse with the body wall.